A communication system based on the Internet consists of a protocol stack generally formed of five layers. The structure of the protocol stack is as illustrated in FIG. 1.
FIG. 1 is a view illustrating an example of a commonly used Internet protocol stack.
Referring to FIG. 1, the uppermost layer of the protocol stack is an application layer for supporting a network application such as file transfer protocol (FTP), a hypertext transfer protocol (HTTP), a simple mail transfer protocol (SMTP), and a real-time transport protocol (RTP). Next, there exist a transport layer for performing data transmission between hosts using a transmission control protocol (TCP) and a user datagram protocol (UDP) and a network layer for setting a path through data is transmitted from source to destination by an IP protocol. In addition, the protocol stack consists of a link layer for performing data transmission between peripheral networks and medium access control (MAC) through a PPP/Ethernet protocol and a physical layer that is the lowermost layer for transmitting data in units of bits using wired media or wireless media.
FIG. 2 is a view illustrating the operations of the respective layers for transmitting commonly used data.
Referring to FIG. 2, the transport layer of a transmitting part adds header information to a message payload received from the application layer that is an upper layer to generate a new data unit. The transport layer transmits the generated data unit to the network layer that is a lower layer. The network layer adds the header information used by the network layer to the data received from the transport layer to generate a new data unit and transmits the generated data unit to the link layer that is a lower layer. The link layer adds the header information used by the link layer to the data received from an upper layer to generate a new data unit and transmits the generated data unit to the physical layer that is a lower layer. The physical layer transmits the data unit received from the link layer to a receiving part.
The physical layer of the receiving part receives a data unit from the transmitting part to transmit the received data unit to the link layer that is the upper layer of the physical layer. The receiving part processes the headers added to the respective layers and transmits the message payload obtained by removing the headers to the upper layer. Data transmission and reception between the transmitting part and the receiving part are performed through the above processes.
In order to perform data transmission and reception between the transmitting part and the receiving part as illustrated in FIG. 2, the respective layers add protocol headers to perform control functions such as data addressing, routing, forwarding, and data re-transmission.
FIG. 3 illustrates a protocol layer model defined by a wireless mobile communication system based on the commonly used institute of electrical and electronics engineers (IEEE) 802.16 system.
Referring to FIG. 3, a MAC layer that belongs to the link layer may consist of three sub layers. First, a service-specific convergence sub layer (CS) may transform or map the data of an external network that is received through a CS service access point (SAP) to the MAC service data units (SDU) of a MAC common part sub layer (CPS). This layer may distinguish the SDUs of the external network from each other and then, may relate a corresponding MAC service flow identifier (SFID) to a connection identifier (CID).
Then, the MAC CPS as a layer for providing the core functions of the MAC such as system access, bandwidth assignment, and connection set and management receives data classified by specific MAC connection from various CSs through a MAC SAP.
At this time, quality of service (QoS) may be applied to data transmission and scheduling through the physical layer.
In addition, a security sub layer may provide authentication, security key exchange, and encoding functions.
The MAC layer is realized by concept of transport connection as a connection-oriented service. When a terminal is registered in a system, service flow may be defined by a negotiation between the terminal and the system.
When service request is changed, new connection may be set. Here, the transport connection defines mapping between peer convergence processes that use the MAC and the service flow and the service flow defines the QoS parameters of the MAC PDU exchanged in corresponding connection.
The service flow in the transport connection performs the core functions in operating the MAC protocol and provides mechanism for managing the QoS of an upward link and a downward link. In particular, service flows may be combined with processes of assigning bandwidth.
In the common IEEE 802.16 system, a terminal may have a universal MAC address having the length of 48 bits in each wireless interface. The address may be used for uniquely defining the wireless interface of the terminal and for setting the access of the terminal in an initial ranging process. Since a base station verifies terminals by different identifiers (ID), the universal MAC address may be used as a part of an authentication process.
The respective connections may be distinguished from each other by a connection identifier (CID) having the length of 16 bits. While the initialization of the terminal is performed, two pairs of management connections (an upward link and a downward link) are set between the terminal and the base station and three pairs may be selectively used including the management connection.
FIG. 4 illustrates processes of a common wireless access system generating MAC PDUs for a plurality of MAC SDUs.
Referring to FIG. 4, it is assumed that MAC SDUs for a number of, for example, three different flow connections for one terminal are transmitted. At this time, in order to generate a medium access control packet data unit (MAC PDU), the base station or the terminal may use different generic MAC headers (GMH) for the respective connections
In the case where there exist MAC SDUs for different three connections, when the GMHs are attached to the MAC SDUs, three MAC PDUs may be formed. In the case of a connection in which security association (SA) is activated, security information items on corresponding MAC PDUs may be included in the respective MAC PDUs. At this time, the security information on the MAC PDU may consist of a pair of packet numbers (PN) and integrity check values (ICV).
FIG. 5 illustrates the format of a common MAC PDU when a broadcast control message is transmitted.
Referring to FIG. 5, the MAC PDU may process the connection payload information of a connection. The MAC CPS forms the MAC PDUs. The format of a common MAC PDU for the transmission of a broadcast MAC control message may be formed like the MAC PDU 501 of FIG. 5.
The MAC PDU 501 includes a GMH 502, an extended header (EH) 503, and a payload 504. The payload consists of payloads from at least one connection. Each of the connection payloads consists of at least one MAC SDU or MAC SDU fragment received from a CS layer for a corresponding connection.
When a broadcast MAC control message is transmitted, the format of the GMH may be formed like the GMH 502 of FIG. 5. The GMH 502 includes a flow ID for distinguishing connections from each other. In addition, the GMH 502 includes an EH field that represents whether an EH exists in the MAC PDU. In addition, the GMH 502 includes a length field that represents the length of the payload of the MAC PDU. The size of the GMH is fixed.
In addition, when the broadcast MAC control message is transmitted, although not shown in FIG. 5, the format of the EH includes an EH type that represents the type of the EH and an EH body field for a specific content type. The MAC PDU includes a GMH of a fixed size.
In general, a broadcast message informs resource allocation to a burst to which the broadcast message is transmitted by a MAP through a non-user specific A-MAP (or by a broadcast STID performing blind decoding). At this time, when a plurality of broadcast messages are transmitted from one sub frame, since the plurality of broadcast messages are transmitted using the same flow ID, the plurality of broadcast messages cannot be multiplexed and are to be concatenated by one burst to be transmitted.
A control message may be transmitted as a broadcast message, a multicast message, or a unicast message. The types of all of the control messages are defined by the first fields of the messages. Therefore, the terminal may know which kind of broadcast message is transmitted after payload is decoded.
That is, it is possible to check which type of message is transmitted from the base station through the first field of the payload of the MAC PDU.
Therefore, when there exists the MAC PDU transmitted to the STID that represents the broadcast message, all of the broadcast messages transmitted from a corresponding sub frame are decoded.
However, since all of the broadcast messages are transmitted to the same flow ID in a resource region known through the non-user specific MAP (or the broadcast STID) and the broadcast message may detect that the MAC PDU transmitted to corresponding resource is the broadcast message through the non-user specific MAP, actually, the flow ID transmitted from the GMH of the broadcast message may be a meaningless value.
When a multiple broadcast message is transmitted from one sub frame, the terminal must decode a message that is not necessary to be received since the message is the broadcast message. Therefore, the overhead of the terminal is increased.